Iodine-containing oligohexafluoropropylene oxides of the general formula (IV): ##STR1## wherein Rf is a perfluoroalkyl group having 1 to 10 carbon atoms and letter n is an integer of from 0 to 100 are useful intermediates for use in the synthesis of fluoro resins, fluoro rubbers and fluoro surfactants. However, none of prior art methods for preparing such oligohexafluoropropylene oxides have gained commercial success.
More particularly, iodine-containing oligohexafluoropropylene oxides are prepared as shown by the following reaction scheme by starting with an oligohexafluoropropylene oxide carbonyl fluoride of the following formula (II), subjecting the reactant to hydrolysis to form a carboxylic acid, reacting it with silver oxide to form a silver salt, and subjecting the salt to pyrolysis in the presence of iodine to thereby form an iodine-containing oligohexafluoropropylene oxide of the following formula (IV) (see Japanese Patent Application Kokai No. 30441/1988). ##STR2##
However, several problems must be solved before this process can be commercially practiced. The end product, iodine-containing oligohexafluoropropylene oxide is recovered only in yields of about 70 to 85%. The intermediate or silver salt is often a solid which is difficult to handle. The use of expensive silver necessitates silver recovery from a commercial standpoint. The overall process involves three steps, during which toxic hydrogen fluoride evolves. Pyrolysis reaction must be carried out before the end product can be obtained. Also, economical problems arise from the use of expensive reactants and increased installation cost.
There is a need for the commercially advantageous manufacture of iodine-containing oligohexafluoropropylene oxides while overcoming the above-mentioned problems.